Electromagnetic instrument.



W. K. MENNS.

ELECTROMAGNETIC INSTRUMENT.

I APPLIGATION FILED MAR.24,1911. l ggg ggg Patented June 18,1912.

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ZWW/ QQ tint i amass is Wrhli'llfiifi K. 0F 'ZMALDEN, MASSACHUSETTS, ASSIGNOR TO GHARLES H. EEAEESON, 0F BBOOELINE, MASSACHUSETTS.

ELEGTBOMAGNETIU INSTRUMENT! ea set).

subject of King George V of England, re-

siding at Maiden, in the county of Middleand State of Massachusetts, have invented new and useful Improvements in Electromagnetic Instruments, of which the following is a specification.

This invention relates to improvements in electroanagnetic instruments such as tachometers, speed indicators and electricity meters'and particularly to devices of this class in which the indicating element is moved by a disk of low electrical resistance placed Within the field of a magnetic rotor which, when rotated, sets up lines of magneticiforce flowing through the disk producing a braking effect which tends to rotate the disk with the rotor, there being provided a spring restraining the disk and acting to return it to its initial or zero position when the magnetic rotor ceases to rotate. The variable rotation of the magnetic rotor due to the variable speed of the machine to which it is connected to be driven actsto move the indicating element to varying position corresponding to the speed of the machine, there being provided a suitable graduated scale by means of which the speed may be read. 'Heretofore, such instruments 'have heen found to be very seriously affected in the r accuracy by. variations 1n temperature. Heretofore, attempts have been made to overcome these inaccuracies, but thus far the means employedfor con'lpensating for the changes of temperature have thus proven to be inaccurate.

A. characteristic of magnets is that the intensity of the magneticfield does not vary in direct proportion to the distance traveled toward or away, from the magnet or, in other Words, in moving an object in the magnetic field away from the magnet during the first thousandth of an inch of movement, the

magnetic force does not decrease as much as it does during the second thousandth of an inch of movement. It has been found that thermostats employed for compensating for changes ot temperature hile they do correctithe reading of the instrument to a certain extentyet it the influence of the their-i mostat is correct for normal and below nor mal temperatures its influence is tdo great tor temperatures abovenormal and as a re; salt the thermostat-produces an overrec- Specification Letters ratent.

Application filed March 24,1911. Serial No. 616,640.

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tion so to speak. It has also been found that where the thermostat is of the bi-metallic type in which one of the metals is steel, the thermostat if placed within the magnetic field or if connected by a magnetic part to the field mass is influenced by the magnetism to such a'marked degree as to render the thermostat so inaccurate and unreliable as to be practically inoperative for the purpose of compensating for changes of temperature.

The object of my invention is to provide a simple, inexpensive and reliable means for compensating for changes oftemperatureby changing the relative location of the rotating magnet and pivoted disk, or the relative location of the magnet and the field member, or the relative locationof the magnet, the pivoted disk and the field member.

The object of my invention is to provide correcting the action of the thermostat or, in other words, causing the thermostat to exerta compensating influence upon the instrument in proportion as the intensity oi the magnetic field diminishes as the disk or field ring or both disk and field ring ap proach or recede from the magnet, th s object being attained preferably by providing means for resisting the movement of the thermostat in one directionfrom its normal position. vents the thermostat from moving the disk and field mass too rapidly ortoo far to ward the magnet as the temperature rises above normal.

To these ends, my invention consistsin the novel featuresiifcmistructioii and in the combination and arrangement of parts set forth in the Eolloiving" specification an(l]p'articularly pointed out in the claims.

Referring tothe drawingsr-Figure 1 is a plan of an electromagnetic indicating instrument embodying my invention, the cover being removed. Fig. 2 is .a sectional view taken on line 22 of Fig. 1.

Like numerals refer to like parts in both viewsof the drawing.

In the drawings, I have shown an electromagnetic vspeedometer or tachometer of the Warner type, although it will be clearly understood that my invention is applicable netic instrument.

5 is the outer c as,1 ng,.6 e magnetic rotor,

7 the .tield ring or field mass, and v8 .is a

member consisting of a .disk of lorv elec- In other words, this means prcrical resi an e i te posed etwe n .Ithe r1 netic rotor stops.

magnetic rotor and the fieldv member and attixed to a shaft 9 pivotedin bearings--10 and 11 so as to swing freely on the same I axis on which therotor 6 rotates. This disk is provided with a vertical flange 12 which. in practice, will be provided with suitable" numerals on its periphery in a well known manner, as shown iii-the patent to Warner, 823.237, dated June '12, 1906, which numerals are viewed through a glass window 13. The bearings 10- and 11 and the field ring 7 are mounted in an inner casingH which is of non-ferrous material. When the rotor (S is rotated, it generates eddy currents in the disk 8, the reaction of these currents on the magnetic field of the rotor sup-plying a torque to the disk so that the magnetic pull thereon tends to rotate the disk with the rotor. The disk, however, is restrained by a suitable yielding means consisting of a hair spring 15 secured at its inner coil to the shaft 9 and at its outer end to a suitable fixed pin 16. This spring acts to keep the indicator steady atall speeds and return it to zero when the mag The field ring 7 serves to concentrate and conserve the magnetism, thereby insuring a more powerful pull on the pivoted disk 8.

Thus far, the construction and operation are well known to those skilled in this art. I willnow proceed to describe the means whereby I am enabled to compensate forchanges of temperature whereby the in-aecuracies of the instrument mvin'g to variations dftemperatnre are obviated.

The casing 14 which contains the hold ring 7 and the pivoted disk 8 is supportedby one or more thermostats preferably of the bi-metallic laminated type and preferably two, as sl1o\\'n.whicl1 are designated by the immerals 17 and 18.'each of these the!- mostats being preferably composed of two lamina. the upper lamina of each thermostat being formed of a material having a greater i-oetiieient of expansion than the lower lamina. In practice. the best results have been secured with zincfor theupper lamina and steel for the lower lamina,'the two strips of metal being secured togetherin any suitable manner as by means of rivets 19 and 20.

The thermostat 17 is supported at its left hand end upon a suitable fixed support as,

for example, a ring 21 forming a part of the casing 5 and in like manner, the right hand end m"- the thermostat 18 is supported! upon the opposite side of said rin This ring is provided with an inwardly extending tinge 22 to which the thermostatsl'? and 18 are rigidly secured by means of screws 23 and 24, respectively. The other endsof the thermostats are unsupported and from these unsupported ends the easing 14 is suspended by suitable 'means such,

for example, as screws 2.) and .26 screwed into the casing 14. In this wa v, smce the casing is supported at both sides.it will move in a direction parallel to the vertical axis thereof.

The lamime of'the thermostats 17 and 18 are so-proportioned that at a normal temperature, say F., at which the inst-rument graduated. the thermostats are straight and the readings of the instrument are made correct for all speeds and when "the temperature varies above and below normal, the thermostats rise or fall, as the case may be, at their free ends, owing to the unequal expansion and. contraction of the strips of metal composing each thermostat, thus raising or lowering the ea'slng 14 together with the ring 7 and disk .8, it being understood that when the temperature falls below normal the casing is raised and when.

the temperature goesabove normal the casing is lowered. tensity -of the magneti field does not vary in direct proportion to the distance traveled toward or away from the magnet. It follows that the compe'nsating \intlnence of the-- As before stated, the inthermostats if correct for temperatures below 7 0 will be too great at temperatures above 70, and that some means must be provided to cause the thermostats tomove the pivoted disk exactly in proportioirto the intensity of the magnetic field. I accomplish this, preferably providing means for imposing a restraint; upon that movement of the thernmstats during which the disk 8 and field ring 7 are carri'edto- ,ward the magnetic rotor 6, but preferably leaving the thermostat free as to upward movement, this result being arrlved at in a very s mple manner by arranging the support for aeh thermostat so that the :dis-

tance from the free end thereofto its abso-,

lutely fixed point is greater than the dis-- tance from the free end tov the extremity of 7 the support. Thus it will be seen that the supporting flange22 extends :along the thermostat l8 beyond I the sore? 24, and, therefore, when the thermostat bends downwardly it is restrained to a certain extent by that portion ofthe flange 22 which is located between its edge and the pointwhere the thermostat is secured to the flange by a screw, but when the thermostat rises it bends from the point Where it is attached to the flange by its'screw'andthe flange does not restrain the thermostat on its upward movement in the manner in which it is restrained in its downward movement. Moreover, I preferably provide an, additional means consisting of elastiirplates 27' and 2S interposed betn een the tower faces of the thermostats 17 and 18, respectively,"

and the up er face of the flan; "e'22. These plates pre erably are not absolutely unroae'eao what resilient and their thickness and length are carefully proportioned so that they impose the proper degree of restraint upon the downward movement of the thermostats, or in other words, when the temperature rises above normaland the thermostats move downwardly to carry the disk and field ring toward the magnet, the then mostats are prevented from moving the dislt and field mass too rapidly or too far toward the magnet as the temperature rises above normal. V

Another important feature of my inven tion consists in the placing of the thermostats entirely outside of the intlu'cnce ot' the magnet and the field mass so as to be entirely uninfluenced thereby. it being understood that the thermostats are composed partly of steel and if placed within the magnetic field would be influenced by the mag} netism to such a marked degree as to render the thermostat so inaccurate and unreliable as to be practically inoperative.

Another important feature of my invention. consists in moving not only the field ring 7 toward the magnetic rotor (l. but the disk 8 as well. as l have found by moving; tl'ie'disl; a less amount of travel is required than where the vin alone is moved and by moving both the ring and dislc a still less amount of travel is required, or, in other words, by moving the disk and the ring relative to the magnet the movement required is well within the capability of the thermostats.

Having thus described my invention.what

said nunuhcr, and means to impose a retit) straint upon saidthermostat in its operative movement in carrying said member toward the mint ot jreatest intensity of said ma netic field.

3. An electro-magnetic instrument haring, "in ombination. a rotatable magnet tor producing a magnetic field. a metal member mounted to oscillate in said field. a laminated thermostat. means connecting said thermostat. to said member. and means to support said thermostat. said means having: provision for restraining said thermostat in its operative movement in carrying said member toward the point. of greatest intensity of said magnetic field.

4.-.\n electromagnetic instrument having, in (.OfilbillfllIlOIl, a rotatable magnet for producing a magnetic field, a metal member mounted to oscillate in said field. a laminated thcrn'iostat. means connecting said thermostat to said member. and means engaging one face of -aid thermostat and re.- straining the same in its operative movement in one direction.

An electro-magnetic instrument having, in combination. a rotatable magnet for producing a. magnetic field. a metal member mounted to oscillate in said field. a laminated thermostat connected to said member for' changing the relative location ot said member and said tin, gnet, to compensate for changes of temperature..means to hold one' end of said thermostat in fixed position, said means engagingone face of said thermostat adjacent to said end for restraining said thermostat in its operative movement in one direction, and means forming an operative connection between the other end of said thermostat and said member.

6. An electromagnetic instrument having, in combination, means for producing a magnetic field. a metal member mounted to oscillate in said field, a thermostat, means connecting said thern'iostat to said member. and means'including an elastic device for yieldingly restraining said thermostat in one direction of its operative movement.

7. An; electro-magnetic instrument having, in'coml'iinatitm, means tor producing a magnetic field. a metal meml'er mounted to oscillate in said field, a tlie'niostat. means connecting said thermostat to said member. and an elastic plate engaging one. face of said thermostat and restraining the same in one. direction of its operative movement.

8. An electro-magnetic instrument hav ing, in combination, a field 'mass and a cooperating rotatable magnet for producing a n'iagnetic field, a metal member mounted to oscillate in said field, thermostatic means, means connecting said thermostatic means to said member and to said field mass, and means for rest raining said thermostat in one direction of its operative movement.

in testimony whereof I have hereunto set my hand in presence of two subscribing \vitnesses.

VA UIER K. lilENNE-l.

lvitnesses WM/rm: l5. Motlmw, liol'is A. .lonrs llt) 

